Miscibility scattering studies

Mehta, R., and Dadmun, M. D. 2006. Small angle neutron scattering studies on miscible blends of poly(styrene-rfln-vinyl phenol) with liquid ciystalline polyurethane. Macromolecules 39 8799-8807. 

The main experimental techniques used to study the failure processes at the scale of a chain have involved the use of deuterated polymers, particularly copolymers, at the interface and the measurement of the amounts of the deuterated copolymers at each of the fracture surfaces. The presence and quantity of the deuterated copolymer has typically been measured using forward recoil ion scattering (FRES) or secondary ion mass spectroscopy (SIMS). The technique was originally used in a study of the effects of placing polystyrene-polymethyl methacrylate (PS-PMMA) block copolymers of total molecular weight of 200,000 Da at an interface between polyphenylene ether (PPE or PPO) and PMMA copolymers [1]. The PS block is miscible in the PPE. The use of copolymers where just the PS block was deuterated and copolymers where just the PMMA block was deuterated showed that, when the interface was fractured, the copolymer molecules all broke close to their junction points The basic idea of this technique is shown in Fig, I. 

The phase structure of structurally different polyethylene blends was reviewed by Mandelkem et al. [1996]. It was noted that smaU-angle neutron scattering (SANS) can establish the homogeneity in the melt. The question of cociystaUinity can be assessed by calorimetry as well as SANS. Alamo et al. [1997] utilized SANS to study the phase behavior of blends of linear and branched polyethylene and demonstrated miscibility at < 4 branches/100 backbone carbons and phase separation > 8. 

Kyu et al. (2) and Ree et al. (3,5) studied blends of LLDPE-B (114,000 M , 4.50 PDI, and 18 ethyl branches per 1000 backbone carbons) and LDPE (286,000 M, 15.98 PDI, and 26 short and 1.6 long branches per 1000 backbone carbons) using in situ small-angle light scattering (SALS) and DSC and found that these blends are miscible across the whole composition range. Similar miscibihty results were reported for LDPE blends with LLDPE-B and LLDPE-O polymers by other research groups. The DSC and DMTA analysis of Lee et al. (43) confirmed that the blends of LLDPEs (LLDPE-B 89,300 M, 3.8 PDI, and 15-16 branches per 1000 backbone carbons LLDPE-O 93,100 M, 3.6 PDI, and 15-16 branches per 1000 backbone carbons) and LDPEs (73,000-98,000 and 8.7-9.2 PDI 32-34 branches per 1000... 

Her current research interests include studies of miscibility and physical aging in blends, nanophase separation in polymers with long side-chains, polymer dynamics, liquid crystalline polymers, composites, and systems containing nanoparticles. A common feature of these studies is the use of scattering techniques, especially neutron scattering, to study the local structure, conformation, and dynamics in polymers. She has written various reviews and book chapters in this area and has served on selection panels to allocate beam time at neutron facilities. 

A wide range of methods can be used to study polymer miscibility. One of the simplest relies on the fact that materials that do not absorb light also do not scatter it if they are homogeneous down to a scale below that of the wavelength but do scatter it if they are not. If a blend of two polymers that... 

Important morphological questions about miscible blends in which one or both components have crystallized concern the nature of the overall crystalline texture and the location of the amorphous material. A number of recent publications have sought answers to these questions for particular systems. Early microscopy studies showed that noncrystallizable diluents increased the coarseness of the spherulites of the crystallizable components (21,22) however, more recent scattering experiments have been able to determine more detailed information. 

Microscopies and scattering techniques [10,12] are used to study the micro-domain size, shape and interface content. TEM has been used in many instances in order to determine the miscibility, or phase segregation. 

Neutron scattering is used to study the structure of polymers including polymer chain dimensions, conformations, miscibility of blends structures of block copolymers, semicrystalline polymers and biomacromolecules. The unique property of neutrality makes a neutron an excellent probing tool for... 

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